Fuel injectors having an element to produce turbulence downstream from a sealing seat are German Published Patent Application No. 31 21 572. A cylindrical component having grooves in the cylindrical lateral surface joining the two cylinder end faces is pressed into a borehole situated coaxially with the center line of the fuel injector and leading from a sealing seat to the injection orifice. These grooves are arranged in a spiral and impart a turbulence to the fuel flow when the fuel injector is opened. To implement various fuel jet injection patterns, the grooves may be adapted with regard to their cross-section and pitch. Metering of the injected fuel is also adjusted via the grooves, which are supplemented by the valve-seat member to form closed swirl channels.
Another fuel injector is known from U.S. Pat. No. 4,520,962. Downstream from a ball valve there is a rod in whose surface grooves are provided. These grooves are also arranged in a spiral to produce turbulence and are supplemented by the valve-seat member to form closed swirl channels. An injection orifice which widens in the form of a cone is connected directly downstream.
One disadvantage of the known fuel injectors is the complicated manufacturing of the cylindrical swirl insert. It is expensive and time-consuming to produce the individual swirl grooves. Machining technologies are generally used, and remachining is also necessary because of the burrs formed when cutting the grooves.
The high precision required to prevent the development of a secondary flow path also has a negative effect on cost. The swirl insert is sealed with respect to the valve-scat member by maintaining a high-quality roundness tolerance. This results in a fuel flow directed completely through the swirl channels.